Evaluation and validation of a portable rainfall simulator: comparison of rainfall characteristics

Abstract

The rainfall simulator is an important instrument, successfully applied to investigate several hydrological processes. However, knowledge of properties of simulated rainfall is essential to ensure the application of the rainfall simulator. This equipment must be able to reproduce important characteristics of natural rainfall. Thus, the evaluation of rainfall simulators is essential to validate the equipment and suggest improvements, and these results are fundamental for future research. In this study, we first evaluated the simulated rainfall uniformity based on different operating pressures, rainfall intensities and spray nozzles. Subsequently, the geometry of the experimental parcel was modified to improve rainfall uniformity. Finally, the effects of different sprayer models, operating pressure and rotating disk opening levels on droplet velocity, time-specific kinetic energy (KE t ), intensity and spatial uniformity of simulated rainfall were evaluated. Artificial rain was comparable the natural rain to same intensity. Rainfall intensity was evaluated by collecting water the effective area of the experimental plot. To evaluate the uniformity of rain, the Christiansen uniformity coefficient (CUC) was used. Finally, the drainage rain gauge system was used to quantify the droplet velocity and the KE t of rainfall. The initial plot geometry was 0.7 m x 1.0 m (0.7 m²). However, the equipment was validated for use with a smaller experimental area because the simulated rainfall distribution was much better represented. The results showed that it is possible to reproduce a wide range of rainfall intensities in the desired patterns of uniformity. The simulated rainfall presented drops with velocities in accordance with those of drops of natural rainfall. However, the KE t of simulated rainfall is smaller than the of natural rainfall of the same intensity. It was found that the intensity of rain is influenced by the effect of the spray nozzle, the operating pressure and the opening level of the rotating disc. The droplet velocity, KE t and CUC of the simulated rainfall are influenced by the effects of each spray nozzle, at each operating pressure level and each rotating disc opening level. The rainfall simulator did not show satisfactory performance to reproduce KE t similar to natural rain events, and this may be related to the low speed of the drops at the time of spraying, in addition to the short distance (2.30 m) of displacement to the impact with the soil.